what kind of clouds have lightning?. observing storms from space

What kind of clouds have lightning?

Observing storms from space

Riming electric charge separation

Takahashi and Miyawaki, 2002, JAS

Keys :

Graupel

Temperature

Super-cooled liquid water

Why there is a relationship between radar reflectivity and lightning flash?

Define precipitation features using TRMM Precipitation Radar

Radar Precipitation Features (RPFs)

Contiguous area with rainfall

Properties of precipitation features Flash rateTemperature at 20, 30, 40 dBZecho topsMaximum reflectivity at temperaturesArea of 20, 30, 40 dBZ at temperaturesVolume of 20, 30 40 dBZ at -5oC - -35oCIWC of 20, 30 40 dBZ at -5oC - -35oC

PR echo top height (km)

Population of RPFs and those with lightning

• 1998-2010

Land Coast Open ocean All 36S-36NRPF 3.7 million 6.4m million 11.8 million 22.2 million

With flash 11.5% 2.6% 0.5% 3%

2-D histogram of RPFs and probability with lightning

Temperature of 20 dBZ echo top vs. Temperature of 30 dBZ echo top

Regional variation of lightning probability in precipitation systems

Correlation coefficient to flash rate in precipitation features

maximum reflectivity at altitudes vs. Flash rate

Echo top temperature vs. Flash rate

Correlation coefficient to flash rate in precipitation features

Ocean Coast Land All 36S-36N

Maximum 20 dBZ echo top Temperature

-0.12 -0.18 -0.27 -0.24

Maximum 30 dBZ echo top Temperature

-0.30 -0.36 -0.40 -0.38

Maximum 40 dBZ echo top Temperature

-0.49 -0.50 -0.49 -0.50

Maximum reflectivity does not have good correlation with Flash rate neither ( < 0.5 )

Correlation between radar reflectivity vs. flash rate in precipitation features

Correlation coefficient to flash rate in precipitation features

area of reflectivity at temperatures vs. Flash rate

Solid : land Dotted: ocean

area of reflectivity at temperatures vs. Flash rateauto-correlation among different part of storms removed

Solid : landDotted: ocean

Regional variation of correlations (I)Correlation coefficients

Regional variation of correlations (II)Slope of linear relationship

Summary• Flash rate is best correlated with the volume of the high reflectivity

(> 30 dBZ) in the mixed phase region, confirming the importance of the presence of large particles in the charging process.

• More flashes are generated over land than over ocean given the same volume of 30-35 dBZ in the mixed-phase region.

• There are large regional differences in the correlations between radar reflectivity properties vs. flash rate.

• Even with the similar radar reflectivity profiles to the oceanic systems, it is still easier to have lightning flashes over Amazon. Other factors must play important roles besides the graupel at mixed phase region in the lightning generation.

Relative Contributions of Electrified Shower Clouds and Thunderstorms to the Global Circuit:

Can 10 Years of TRMM Data Help Solve an Old Puzzle?

Fair Weather Charge

• In fair weather there is a natural separation of charge in the atmosphere.

+ + + + +

- - - - -

Upper troposphere ispositively charged.

Ground is negativelycharged.

The atmosphere normally has a voltage gradient of 100

volts/meter…

… which may sound like a lot, but what

happens when you stand one

meter from a 110 volt outlet ?

Old Puzzle / Hypothesis

• 90 years ago“A thundercloud or shower-cloud is the seat of the electromotive force which must cause a current to flow through the cloud between the Earth’s surface and the upper atmosphere... In shower-clouds in which the potentials fall short of what is required to produce lightning discharges, there is no reason to suppose that the vertical currents are of an altogether different order of magnitude.”

------ Wilson (1920)

Carnegie Curve vs. thunder days 80 years ago

Diurnal variation of electric field seems reproduced by the thunder days(after add an arbitrary uniform oceanic storms to bring the amplitude down)

Thunderstorms observed by TRMM

Thunderstorms over different regions have different lightning flash rates

AsianAfricaAmericas

Carnegie curve vs. flash count

Good correlation in phase, but much higher amplitudeSame as pointed out by Bailey et al. 2007

Carnegie curve vs. rainfall in thunderstorms

Good correlation in both phase and amplitude

Diurnal variation of flashes Asian

Africa

Americas

Diurnal variation of rainfall in thunderstorms

Asian

Africa

Americas

Vostok electric field vs. rainfall in thunderstorms

Good correlation betweenThunderstorm rain vs. electric field in different seasons

DJF Vostok electric field might be contaminated by weathers

End of story?

• It seems that the diurnal variation of rainfall in thunderstorms has a very good correlation with the Carnegie curve both in the phase and the amplitude.

• However, this is not the end of the story. What about the shower clouds without lightning as mentioned by Wilson 90 years ago?

ER-2 overflight of Emily

In-situ storm current observationsStorm current from 850 ER-2 overflights Courtesy of Mach et al. 2010

A VERY rough way to identify the electrified shower clouds

30 dBZ echo top colder than -10oC over land, -17oC over ocean

Rainfall from thunderstorms, electrified show clouds and others

Carnegie vs. electrified shower clouds

Thunderstorm + electrified shower?

A different approach define convective cells

Three “cell” definitions:

• Convective pixels(red color fill)

• 40 dBZ pixels in any levels (black line)

• 30 dBZ pixels at 6 km (white line)

Global distribution of convective cells

(Solid line) Rain in cells defined by 30 dBZ at 6 km has the best correlation

Electric field vs. Rainfall from convective cells defined by area of 30 dBZ at 6km

Summary of the Carnegie curve• With more observations available today, we have better tools

to play the same game as Whipple (1929) played 80 years ago: relating the diurnal variation of thunderstorms to that of the electric field.

• Diurnal variation of rainfall from thunderstorms has a good correlation with the Carnegie curve both in the phase and the amplitude.

• The role of electrified shower clouds is still hard to describe due to the difficulty of identifying them and quantifying the electric field that they contribute.

• A different approach of adding convective cells gives more hints to this puzzle.

Let’s talk about the final project• Written reports have to be submitted to me in e-mail before

end of Tuesday Feb 26. Late report is not accepted. If you insist to give me a paper report, you have to hand the report to me on Monday Dec 25.

• We have 8 studentsEach one have about 10 minutes of presentation and a few minutes for questions.

So we need 2 class time. We do a lottery on who present first.

If you have presentation on the day, come to classroom 5 minutes early to upload your slides onto my laptop.